Heat shock/stress proteins help to protect cells from increases in temperature and other environmental stresses and serve as chaperones of other proteins. This probably occurs by the heat shock proteins binding to short amino acid recognition sequences in other proteins, thereby causing local conformational changes that restrict additional interactions by such proteins. Spermatogenic cells must be maintained 4-5 degrees below body temperature to develop normally. We are studying the relationship between regulation of expression of Hsp70 heat shock genes in spermatogenic cells and their particular sensitivity to heat and certain environmental agents. The Hsp70 genes are members of one of the four multigene families encoding heat shock proteins. Two of these genes (Hsp70.2 and Hsc70t) are expressed only in spermatogenic cells, where they are regulated developmentally and produce abundant protein. the Hsp70.2 gene is expressed predominantly during the meotic phase of spermatogenesis, while the Hsc70t gene is expressed only during the post- meotic phase. We hypothesize that the proteins encoded by Hsp70.2 and Hsc70t are required by spermatogenic cells to chaperone proteins required for unique meiotic and post-meiotic events, respectively. However, two other genes in this family (Hsp70.1 and Hsp70.3) that are expressed vigorously in response to the shock in most cells, are expressed sparsely in heat-shocked spermatogenic cells. We hypothesize that the limited expression of these genes in spermatogenic cells leaves them particularly sensitive to environmental insults.